A variety of therapeutically-useful intra-body electrostimulation techniques have been employed by physicians to treat both acute and chronic patient conditions. Electrostimulation of soft muscle tissue may be used, for instance, to elicit contractile behavior, or to inhibit such contractile activation.
In particular, electrostimulation is commonly used for cardiac rhythm management. Cardiac rhythm management devices include, for example, pacemakers, cardiac resynchronization therapy devices, and cardioverter defibrillators. Cardiac rhythm management devices can be used to treat conditions such as atrial or ventricular tachycardia, atrial or ventricular fibrillation, bradycardia, and congestive heart failure.
An example of an application of a cardiac rhythm management device includes a battery-operated pulse-generator assembly subcutaneously implanted in the pectoral region, connected to one or more implantable leads deployed through the vasculature using a catheter-based delivery system to locations either within one or more of the heart chambers, or within one of the great veins of the heart.
Implantable flexible leads include one or more exposed electrodes to directly stimulate cardiac tissue, or to sense potentials developed across the electrodes by the tissue (e.g., for sensing intrinsic cardiac activity, or sensing the evoked response to the application of electrostimulus). Tissue growth occurs, and frequently surrounds the area of the electrode in contact with tissue. This may result in the beneficial effect of reducing the required electrostimulus threshold to achieve the desired response, but also presents challenges should the necessity arise to re-position or remove the lead. This may preclude the usage of multiple leads in certain locations.
Epicardial stimulus locations are also sometimes used, for instance during times when acute pacing therapy is desired, associated with other medical procedures, and where access is easily obtained to the pericardial cavity.